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The studies were performed in hypertensive rats (SHR strain) during the period of hypertension development (7-8 weeks) and stable high blood pressure (16-17 weeks) and in normotensive rats (WKY strain) of corresponding ages. The average number of capillaries per square millimeter, the average capillaries diameter, and the capillary network structure following the estimation of capillaries distribution based on capillaries diameter within the following ranges (up to 3, from 3 to 5, from 5 to 7 and from 7 to 9 μm) were investigated using the morphological approach. The average diameter of capillaries and capillary network structure in SHRs during the development of hypertension did not differ from the respective values in WKY rats of the same age. SHR rats showed disturbed microvascularisation by structural and functional rarefaction in the stable high blood pressure period, which was manifested in lower average capillaries density and average capillaries diameter as well as in substantial (2.5 times) increase in plasmatic capillaries as compared to WKY rats of the same age.

The dynamics of arterial blood pressure and hematological parameters (RBC volume, RBC count, hematocrit) in young rats SHR and WKY strains in the period from the 5th to the 8th week after birth was investigated. At the age of 5 weeks, the levels of arterial blood pressure in rats studied strains were not significantly different. Starting from 6 weeks, systolic and diastolic blood pressure in SHR rats were significantly higher than the corresponding values of WKY rats of the same age. During the entire period of observation (from the 5th to 8th week) the number of red blood cells and hematocrit in SHR rats was significantly increased compared with the value of these parameters in WKY rats. Probably, an increased hematocrit can be one of the reasons of increasing the blood pressure in the early stages of hypertension development.